1. Field of the Invention
The present invention relates to a single-chip light-emitting diode (LED), and particularly, to a single-chip LED with three spectrums of red, blue and green wavelengths.
2. Description of the Related Art
In recent years, there is an increasing demand for full color display electronic products, such as mobile phones, digital cameras, digital camcorders, personal digital assistants (PDAs) or the portable computers and the like, to be light and small as well as power-saving. Therefore, conventional application of a cold cathode fluorescent lamp (CCFL) as the backlight source of the LDC screen may fail to meet the property required by the design, and it is desirable to develop a new backlight source for the LCD screen.
At present, in the full color LCD technology, the designs for either the STN-LCD or the TFT-LCD and the like employ a white light backlight source, and three pixels of red, blue and green may be generated by controlling the lights passing through the RGB Color filter. Traditionally, a white light source employs a CCFL as the backlight source of the LCD screen, but due to its high power consumption, the CCFL has a large volume, and in use the direct current (DC) should be inverted to AC voltage by the inverter. Moreover, CCFL causes mercury pollution to the environment. Therefore, for the small and medium sized portable electronic products, CCFL is not the best choice for a backlight source.
Therefore, the technicians began to consider using LED instead of CCFL, since LED has various advantages of small volume, low power consumption and no environmental contaminations, and it may obtain a better color-rendering performance through modulating the wavelengths of the red, blue and green lights.
The earliest conventional technique is to provide three wavelengths of the red, blue and green lights using the red, blue and green chips package. Theoretically, this method is the most preferred choice for the LCD back light source. Because the red, blue and green lights are provided directly, no red, blue and green color filters are needed to generate the desired light source. However, since the red light material differs from the blue and green light material, and according to this method, the circuit is complex and expensive, it is difficult to achieve the consistency of the light and color, and the attenuation rates of the three colors varying from each other lead to an unstable quality, so that the operation complexity and the cost of this method are much higher than the CCFL, and therefore it is not the best choice for the portable electronic backlight source.
The technology used for a majority of small sized LCD backlight sources in the market is the white light element technology developed by Nichia Chemical, with reference to ROC patent certificate No. 383508 and its U.S. equivalent U.S. Pat. No. 5,998,925. In the white light element technology, a blue LED is packaged together with fluorescent powder of its complementary color, and after the fluorescent powder of its complementary color is excited by the blue light, the generated complementary color for blue light is blended with the remaining blue light unabsorbed by the fluorescent powder, thus to generate the white light source which may be used as the white backlight source. Because the spectrum of the complementary color for blue light is mainly yellow wavelength, the ratio of the desired green to the red light source resulted from the color filter is not high, thereby leading to a problem of insufficient light intensity on the LCD backlight source.
Furthermore, the ROC patent certificate No. 172159 discloses a white LED element with the spectrums of three wavelengths, and a method which uses a UV LED to excite the red, blue and green fluorescent powder. In this method, the luminance performance is poor, since the UV AlGaN LED has a short life. Furthermore, three kinds of fluorescent powders with different photoelectrical properties and lives are simultaneously used so that the color and life reliability decreases. In addition, the UV light has to excite the fluorescent powders of three colors at a time.
Moreover, the ROC patent certificate No. 563261 discloses that a blue LED is used to excite the green and red fluorescent powder. Because the absorption and the conversion rates of the majority of red and green fluorescent powders for the blue light are rather poor, the light intensity is insufficient when these two kinds of fluorescent powders are excited by a single blue light source at a time.
Therefore, it is necessary to provide a single-chip LED with three luminescent spectrums of red, blue and green wavelengths to solve the above mentioned problems.